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Astrometric and Photometric Variability in Quasars

Published online by Cambridge University Press:  03 June 2010

A. H. Andrei
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil Email: oat1@on.br Observatório do Valongo, UFRJ, Brazil
S. Bouquillon
Affiliation:
SYRTE/Observatoire de Paris, France
J. L. Penna
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil Email: oat1@on.br
F. Taris
Affiliation:
SYRTE/Observatoire de Paris, France
S. Anton
Affiliation:
Centro de Investigação em Ciencias Geo-Espaciais/FCUP, Portugal
J. Souchay
Affiliation:
SYRTE/Observatoire de Paris, France
J. I. B. Camargo
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil Email: oat1@on.br
D. N. da Silva Neto
Affiliation:
Universidade Estadual da Zona Oeste-BR
R. Vieira Martins
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil Email: oat1@on.br
M. Assafin
Affiliation:
Observatório do Valongo, UFRJ, Brazil
S. dos Reis Carvalho Pinto
Affiliation:
Observatório Nacional/MCT, R. Gal. Jose Cristino 77, Rio de Janeiro, Brazil Email: oat1@on.br Universidade Gama Filho, Brazil
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Quasars are the choicest objects to define a quasi-inertial reference frame. At the same time, they are active galactic nuclei powered by a massive black hole. As the astrometric precision of ground-based optical observations approaches the limit set by the forthcoming GAIA mission, astrometric stability can be investigated. Though the optical emission from the core region usually exceeds the other components by a factor of a hundred, the variability of those components must surely imply some measure of variability of the astrometric baricenter. Whether this is confirmed or not, it puts important constraints on the relationship of the quasar's central engine to the surrounding distribution of matter. To investigate the correlation between long-term optical variability and what is dubbed as the “random walk” of the astrometric center, a program is being pursued at the WFI/ESO 2.2m. The sample was selected from quasars known to undergo large-amplitude and long-term optical variations (Smith et al. 1993; Teerikorpi 2000). The observations are typically made every two months. The treatment is differential, comparing the quasar position and brightness against a sample of selected stars for which the average relative distances and magnitudes remain constant. The provisional results for four objects bring strong support to the hypothesis of a relationship between astrometric and photometric variability. A full account is provided by Andrei et al. (2009).

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2010

References

Andrei, A. H., Bouquillon, S., Camargo, J. I. B., Penna, J. L., Taris, F., Souchay, J., da Silva Neto, D. N., Vieira Martins, R., & Assafin, M. 2009, in Proceedings of the Journees 2008 Systemes de reference spatio-temporels, ed. Soffel, M. and Capitaine, N., (Paris: Lohrmann-Observatorium and Observatoire de Paris), p. 199Google Scholar
Smith, A. G., Nair, A. D., Leacock, R. J., & Clements, S. D. 1993, AJ, 105, 2, 437CrossRefGoogle Scholar
Teerikorpi, P. 2000, A&A, 353, 77Google Scholar